A lot of people are scared that overpopulation will be a problem. Their reasoning is certainly understandable. There is a finite amount of land, a finite amount of resources, but there can be a continually growing population of people. So eventually people will have to exceed the available land and the resources that we have. To understand why overpopulation is not a problem requires a lot more imagination, an ability to see beyond our intuitive notions. It would help if you read what I wrote regarding emergent complexity here and the relationship between evolution and markets here. These are the key ideas to understand why overpopulation will not be a problem.
First I want to begin by saying the world is nowhere near having too many people. Just drive from New York City to Los Angelos. What do you see? Nothing. It is just empty. People just choose to live at the coasts to be near water. All that space can be made to use. So the fear that we are nearing the last days of a sustainable population is unjustified. We are far from it.
Now to get to the overpopulation hysteria that has many people worried. In mathematics there are a pair of equations, known as the Lotka–Volterra equations, here. These equations (actually they are used as a classic example of non-linear system of differential equations) describe the relationship between predators and prey. The idea is that predators feed on prey. If there is an abundance of prey then the predators will have plentiful of food to eat and therefore increase in their size. There are now even more predators to feed on prey. So the prey population will have to have a higher rate of death than it had before. This will continue to happen until there are few too prey left. But once there are too few prey left, the prey need to be rationed between the predators. And so the predators have difficulty satisfying their need for food. As a result the predator population will start dying out. Once the predator population is low the prey population will now be able to increase in size because there are few predators hunting them. Thus, just like a cycle, we are back to where we started. A small predator population with abundance of prey. And this cycle repeats over and over again. Thus, the predator and prey populations will be periodic functions of time. The Lokta-Volterra equations describe these populations sizes in more mathematical terms. But this is essentially the idea behind the predator-prey cycle.
Where do these periodic population sizes for predators and prey come from? Is there some central planner deciding how much prey to feed to the predators or when the predators eat too much? No. This is all emergent. The basic rules of predators and prey, described above, come together to create a rather complex system of population sizes for the predators and prey.
The question of overpopulation should be analyzed in the same manner as the model between predators and prey. Think of human beings as predators and the resources we use as prey. Now it is true that some of our resources are not renewable, like oil, but our primary resources, like food, are renewable. So there will be a difference between how renewable resources and non-renewable resources operate in relation to our growing population. Prey after all are a renewable resource to the predator, so when we consider non-renewable resources the situation will be a little different. But, as we will see, irrelevant in our conclusion that overpopulation is not an issue to worry about.
If people begin to exceed the available renewable resources then they are essentially predators living off the resources. In such a case there will be a shortage of available resources. Which means that resources would have to be rationed. As a result prices will begin to rise (if the economy is market oriented, not a socially planned market) to adjust for scarcity. In addition, there will not be enough resources to consume so that the rate of human population will decrease. It will continue to decrease at a faster rate as long as there is a growing number of people. Eventually, just like with the predator prey model the human population will start dying out at a faster rate then they are being born. Once the human population is much lower the renewable resources would be able to adjust themselves appropriately and the market will adjust itself appropriately by lowering its prices. Humans will now be able to increase their rate of birth with the abundance of new resources. Thus, it is expected, the relationship between human and renewable resource population will be an increasing-decreasing periodic function of time. Place special attention about the part in which the market will adjust its prices accordingly, this is very important. The relationship between prey and predators does not involve any economics, but with humans there is an additional feature of the market that will remove all danger of overpopulation, this is the adjusting market prices, as we will soon see why.
Now the situation with non-renewable resources is different. Non-renewable resources would not come back. However, as people consume more of these resources the market will adjust to its consumption. As a result there will be raising prices. This is precisely why oil will never run out. Yes, there is a finite amount of oil. But we will never reach a point where everyone is using oil one day and the next we have no more oil anymore, that is just silly economics. Rather oil prices will start raising so high that people will have to more away from using oil as a method of energy. So there will always be oil, but it will not be worth it for extraordinary high prices. The raising prices will impose a cost on people for over consumption. It will become a lot more expensive for people to sustain whatever non-renewable resource that it is. Because of high costs people would not have an incentive to reproduce at the rate they did, and the birth rate will start falling back. Therefore, in both the renewable and non-renewable cases the imposed costs will make people reduce their birth rates.
The market is what comes to our rescue here. People who are worried about overpopulation should have a reason to support free market prices. Market prices tell us if we are over consuming or not. Consider this example. Say people start to use too much paper. There are not enough trees and we begin to lose our forests. So people start to complain, "how dare these paper companies charge us so much money, they are greedy, they are taking advantage of us, prices must be less". So the Federal Reserve maintains artificially low paper prices so that paper is priced the same. But the problem is that the artificially low prices would encourage even more people to engage in over consumption of paper. If prices were allowed to be set by the market they will automatically adjust to the scarcity of paper and as a result the cost for using paper will be too high. People will be careful in how they use their paper. People will now indirectly care about saving the trees by reducing their paper usage. Or perhaps going with plastic paper because it would be cheaper. Whatever the course of action people will take it will move people away from over consuming paper thereby allowing the forests to regenerate. So if you happen to be scared by overpopulation then please realize that the market is on your side here. Allow the market to set prices for resources not the law. Prices really tell us something important.
I know some people even support population control, as scary as that sounds. I doubt they want to go so far as cutting off the penis from all men, but they probably support some tax or fee on people who have many children. But this is not necessary. If there is a population problem then a high cost will be imposed on people who have more children. People will just have no incentive to have many children if it becomes so expensive. And so there is no need to impose fees on them. Of course, if we have a welfare system that would support families than no costs would be imposed by the market on such families removing the incentive not to have children. In today's age with birth control and condoms parents will move away from having many children if they get imposed the market costs for less available resources. So in effect large families are being financially punished for having many children, but without any actual fees. This is why population control is not necessary.
I am not scared of overpopulation. Overpopulation is not a problem in the animal kingdom and will likewise not be a problem with people. These population models all arise from emergent complexity. If in addition we are careful about relying on the market rather than socially planned economies or welfare programs we will incur large costs which will create an incentive for parents not to have many children or possibly none at all. Our values are different today as well. In the past people believed marriage is all about having kids, not anymore, now we value love. I am more scared of being struck by lighting while I masturbate openly in the middle of Lakewood than I am of overpopulation.